Use of a Natural Swamp for Wastewater Treatment.

The purposes of this research were to determine the possibility of using a natural forested swamp for advanced wastewater treatment in coastal Louisiana, and to evaluate the wastewater impact on the ecosystem. The study was performed by comparing two portions of a nutrient deficient swamp separated by a ridge. One portion received secondarily treated municipal wastewater at a rate of $6.3\times10\sp6$ L/day and the other served as a control. Concentrations of BOD$\sb5$, TSS, DO, EC, TDS, pH, N, P, S, CI, K, Ca, Mg, Na and trace metals were monitored. Results showed that the wastewater added nutrients into the swamp. Mean concentrations in the wastewater were 14.6 mg/L for total N and 2.5 mg/L for total P. When wastewater passed through the swamp, tertiary wastewater treatment was achieved. The swamp system reduced 100% of NO$\sb{3\sp{-}}$N, 69% of TKN, and 66% of total P in the wastewater. High N removal efficiency would enable the swamp to work well even if the N loading rate were doubled. However, P removal efficiency was dependent on loading rate and temperature. Trace metals were not a problem because of very low concentrations in this wastewater. The swamp was more efficient in treating wastewater during warm seasons than cool seasons. Study showed that denitrification, soil adsorption, duckweed assimilation and sedimentation-subsidence were the most important processes involved. Soil adsorption and duckweed assimilation were more significant sinks for wastewater nutrients in the winter season than in the warm season. After two years of wastewater application, there were no accumulations of nutrients measured in the sediment except for P. Increases mainly occurred in the surface and near the wastewater inlet. However, the high sedimentation rate in the treated swamp enabled more nutrients to be stored in the sediment than the control swamp. Therefore, the swamp sediment should continue assimilating P for a long time. Introduction of wastewater into the natural swamp has additional benefits of: (1) buffering swamp water quality changes due to litter deposition from strong storms such as hurricanes; (2) mitigating natural nutrient loss from the swamp sediment sink; (3) increasing the vertical accretion rate, which could offset wetland loss